March/April 1996
by Paul Vossen, Farm Advisor, Sonoma County
The chestnut is a unique nut-producing tree that may have some potential as an alternative crop for certain areas. Chestnut trees vary in growth habit, depending on the species, but generally make fairly large, spectacular trees.
Four common species of chestnut have been grown in North America. They exist as pure species, or more commonly, as hybrids of the various species, because they readily cross with one another. It is difficult, in many cases, to distinguish specific species and almost impossible to determine the parentage of the hybrids through visible identification.
There are several varieties that have been selected in each species group, and more recently, breeding programs have produced many hybrids. Following is a list of some of the varieties grown in the United States and their purported characteristics.
Chestnuts have male (staminate) flowers, also called catkins, and female (pistillate) flowers that are attached to the lower portion of some of the catkins. Cross pollination is required since the pollen is often shed before pistillate flowers are receptive. Overlapping male and female bloom from two different varieties is required; pollen is wind transmitted. The cream colored nut "meats" are covered with a thin bitter membrane (pellicle) and dark brown, hard, leathery shell, encased in a prickly burr (involvere). The burr splits at maturity and may contain from one to seven nuts. Nut size, degree of burr separation from the shell, and ease of pellicle removal are very important quality characteristics.
The chestnut is a grain growing on a tree. The nut contains about 40 percent carbohydrate, about 40 percent water, 5 to 10 percent protein, and less than 5 percent oil. It is similar to other starchy foods such as potatoes or rice and other grains.
Traditionally the main use in the United States has been for eating raw or roasted as in "chestnuts roasting in an open fire." The nut is very flavorful and sweet and can be used as an ingredient in turkey stuffing, sweet breads, cakes, soups, stir fry dishes, cereals, or ice cream. Candied nuts are common in Europe. Dried nuts can be ground into flour and used in diets for people with allergies to grains.
Estimates of world production, export/import, and use statistics vary considerably with the source of the statistics. The following statistics are from a talk given in August, 1987, by Michael Burnett of the Chestnut Growers Exchange at the Pacific Northwest Chestnut Congress, Corvallis, Oregon.
Most of our imports are from Italy. The nuts are shipped by boat and are sometimes of inferior quality. We import 10 million pounds; about $20 million worth. Import prices range from $1.50 to $3.00/lb. (average $2.10/lb.).
The United States would need to produce chestnuts on 5,000 acres just to displace imports. Reduced transportation costs and improved local quality should help capture a market. There also seems to be a potential to increase consumption through marketing and promotion programs.
Good judgment indicates that the culture of chestnuts parallels that of walnuts. Chestnuts need well-drained soil to survive and thrive. Deep alluvial soils would be optimum. Soil reaction or pH should be acid, as chestnuts have little tolerance for alkaline soils (optimum pH range 6 to 6.5). Trees could be closely planted to 20 x 20 ft., 25 x 25 ft., or 30 x 30 ft., depending on the tree form and willingness to remove every other tree when crowding occurs. The large timber form trees are less desirable for California nut production. Hedgerow plantings of 9 to 14 ft. x 18 to 25 ft. might work, as it does with some walnut varieties.
Irrigation is required for rapid tree establishment and will most likely improve yields on a competitive commercial basis. It is important to build a large, strong tree as soon as possible.
Chestnut trees most likely will require tree training when young to develop a good modified central leader scaffold system. Good light penetration into lower branches could become important for mature trees to maintain production throughout the tree. Alternate-year pruning may also be feasible.
Fortunately chestnuts are relatively free of pests. The major pests known to attack chestnuts are:
No mechanical system of chestnut harvest has yet been perfected, but most likely would be essential to lower labor costs. Some existing harvesting techniques for other crops such as walnuts, filberts, and processing cherries seem to be adaptable to chestnuts. Chestnuts should be treated more like apples in storage than like other tree nuts. They must be cooled to 32° F as soon as possible. Chestnuts dry out even at high humidity, so protective packaging is needed. Mold inhibiting fungicides and controlled atmosphere storage would most likely improve chestnut quality in long term storage.
Seedling trees are quite variable and definitely not acceptable for commercial production. Seedlings can, however, be used as rootstocks, but only with scion wood from the same tree of origin as the seedling, because of widespread graft incompatibility problems. Grafting of high quality scion varieties onto random seedling trees commonly produces a poor graft union in 1 to 10 years. The normal grafting methods used on other woody species are quite successful with chestnut, especially if callusing is enhanced by temperatures near 80° F, high relative humidity, good aeration, no light, and limited pressure (hot pipe technique). Self rooting the trees is perhaps the best procedure for mass production, through layering, cutting, or tissue culture.
